This invention relates to gas turbines and more particularly to controls which rapidly vary the rotating energy produced by the turbine and yet prevent flameout and changes in temperature which produce thermal shock in the high temperature portion thereof.
When a gas turbine is employed as a prime mover to drive an electrical generator to produce electrical power, or to drive a compressor to pump natural gas in a pipe line, there is no need to provide for rapid variations in load, however, there are other instances where the load on the turbine changes drastically and it is necessary to provide for such load changes. For example, when a gas turbine is employed as a prime mover on a ship and is coupled through a generator and motor to the ship's propellers there may be instances when the propellers tend to drive the turbine through the motor and generator. This would be particularly the case, when the ship is designed for icebreaking. In maneuvering an icebreaker it is somewhat required to operate the ship in crash reversal and in such maneuvers the propellers may drive back through the motors which become generators and drive the generator and the turbine. Under such conditions, the turbine over speeds and the governer attempts to reduce the speed of the turbine by closing the fuel control valve, the fuel-air ratio in the primary zone of the combustion chamber may deviate from the stoichiometric ratio to such an extent as to cause flameout, whereafter the turbine becomes inoperable. If the reduction of fuel is limited to a value which will preclude flameout the turbine over speeds and is tripped by an overspeed condition again rendering it inoperable.
One solution for preventing overspeeding is to provide a fly wheel, which is capable of absorbing a large quantity of energy, however, because of the mass and speeds involved, a large fly wheel is not economical so that a more satisfactory energy absorbing system is desirable.